Sail



July 9, 1968 J. BIRCHILL 3,391,668

SAIL

Filed Jan. 13, 1967 2 Sheets-Sheet 1 INVENTOR. .1056? BIRCH/1. L

July 9, 1968 J. amen-nu. 3,391,658

I SAIL Fil'ed Jan. 15, 1967 2 Sheets-Sheet 2 INVENTOR. J0$PH B/PCH/Ll.

ATWNA'YS.

United States Patent 3,391,668 SAIL Joseph Birchill, 2625 Palos Verdes Drive W., Palos Verdes Estates, Calif. 90275 Filed Jan. 13, 1967, Ser. No. 609,201 18 Claims. (Cl. 114-103) ABSTRACT OF THE DISCLOSURE This invention pertains to a sail of flexible sheet material incorporating a means to improve the performance by preserving the proper contour of the sail under differing conditions. The said includes a chamber inflatable by ram air, which results in a desirable shape for the sail, while lufling is inhibited.

Background of the invention (1) FIELD OF THE INVENTION This invention is in the field of sails for boats.

2) DESCRIPTION OF THE PRIOR ART In the use of conventional sails, dynamic pressure or tension distributions will be such under certain conditions that the sail does not preserve the desired full shape but collapses or flutters. This causes a significant reduction in overall performance. Particularly difficult to combat has been What occurs during operation of the sail in a closehauled or low-angle-of-attack condition. Under these circumstances, the stagnation point moves forwardly to a location near the leading edge or luff of the sail on the lee side. The degree of close-hauled operation is limited because eventually the forward portion of the sail will flutter and performance will be impaired. Also, when the sail is let out to reduce loading under high winds, luffing again will occur. In the use of a spinnaker in a reach, a similar situation prevails, where the windward edge of the sail curls inwardly, eventually collapsing the sail.

Efforts to deal with'the problem of lufiing at once encounter the further requirement that the sail, for efficient operation at higher angles of attack, is best designed with a large camber located forward, which accentuates the luffing difliculty. Current practice is to deal with this com bined problem by employing a mast which will bend in a direction to reduce the fullness of the sail, by arrangements which will allow the reefing of surplus cloth in the luff region, and by control of the tension and associated deformation of the luff. These means are only partially successful and offer only limited performance improvement. Bending masts are sensitive to wind strength and can be applied only to a mainsail.

Further improvement of the sail, to combat luffing and to simultaneously provide a contour suited to eflicient operation generally, has been sought by a variety of means, including employment of rigid or semirigid structures, the contour of which is sometimes adjusted or controlled by mechanical or pneumatic means. Rotatable streamlined masts have been used to define a proper aerodynamic shape and prevent luffing. A related aspect of the problem to which attention has been directed is the reduction of turbulence and drag from the flow of air around the mast. Pairings, usually of rigid or semirigid material, behind the mast have been utilized to improve this condition and also in an effort to prevent lufiing. These expedients have not found general application due to extremely adverse characteristics such as cost, weight aloft, maintenance problems, handling and stowage, and customer acceptance. They require in most cases the replacement of the entire mast and rigging and in some cases an entirely new boat of a different design. A matter 3,391,668 Patented July 9, 1968 of particular importance is that of class rules, which typically preclude such items as rotatable masts or artificial stiffening of the luff, or any extensive or costly modification.

Summary of the invention The present invention attains the desirable objectives mentioned above, particularly with respect to the prevention of lufiing, without any of the above-mentioned adverse characteristics. This is accomplished by providing a sealed chamber of lightweight flexible material such as ordinarily used in sail construction, extending along the leading edge portion, with an air inlet at the head of the sail. The air, having a dynamic pressure resulting from the relative velocity with respect to the boat, may enter the chamber and inflate the material so that it defines an appropriate airfoil shape to improve general performance and reduce drag, when otherwise luffing would occur. A single opening may be provided at the head of the sail to admit the air, with a stiffener around the inlet to hold it open. Alternatively, there may be provided air scoops on either side of the sail, each leading to an aperture that provides entry to the air chamber. A flapper valve may be located beneath each of these openings, or incorporated into the single inlet, so that air flowing in will not be impeded, while the egress of air will be prevented. These valves will act to maintain the internal pressure at the maximum obtained from either of the dual inlets, and at the same time maintain the internal pressure in the event of a momentary drop in wind velocity. Either type of inlet, being integral with the head of the sail, points generally into the relative wind during those conditions of use when it is desired to inflate the chamber, to receive ram air for this purpose. Normally, the chamber extends the full length of the luff of the sail, with the rear edge of the chamber being arcuate and connecting to the forward edge at the top and bottom of the chamber. This configuration helps prevent the entire sail, in particular the chamber walls, from becoming wrinkled and distorted.

The use of a completely flexible material, such as woven sailcloth of the normal type, is of significant importance since the flexible property is employed cooperatively to attain the desired result. While the use of this type of material is generally desired for obtaining easy handling and stowage, maintenance and similar favorable characteristics mentioned above, this invention will function best with a material of maximum flexibility. The airfoil-shaped fabric chamber extending along the leading edge obtains its shape due to a positive pressure differential acting to expand the chamber and the action of tension in a chordwise direction. The differential pressure acting on the walls of the chamber is the result of both the application of full (positive) stagnation pressure to the inside of the chamber and the reduced external pressure resulting from the flow of air over the external curved surface. Thus, any stiffness of the material will act to reduce the curvature of the chamber and adversely affect the pressure differential, which will reduce the effectiveness of this invention.

Under differing operating conditions, the present invention will automatically adapt itself to form an optimum contour, without any necessity to exercise control over the internal pressure acting in the chamber. At very high angles of attack or when running before the wind, the direction of airflow relative to the inlet and the external pres-sure on the windward side of the chamber no longer produce an inflation pressure differential in th chamber. Air contained in the chamber is gradually forced out through a small vent (not shown) or through fabric, seam and valve leakage. Thus, the chamber is deflated and the sail will function as a conventional sail 3 having a full contour which is desirable under these conditions of operation.

An object of this invention is to provide a sail of generally improved performance that is inhibited from collapsing or fluttering.

An additional object of this invention is to provide a sail that can operate at a low angle of attack without lnfling.

Another object of this invention is to provide a sail capable of operation in a close-hauled condition or which may be let out in a high wind without luffing.

A further object of this invention is to provide a means for preserving the shape of a sail using lightweight flexible material, and without the use of stiifeners or other auxiliary devices.

A still further object of this invention is to provide an improved sail having a shape-maintaining arrangement that is of low cost, light weight, and simple operation and maintenance without requiring modification to the mast or other portions of the sail or of the boat.

Yet another object of this invention is to provide a sail having a flexible chamber inflatable by ram air entering an inlet that always is positioned to receive the Wind during those conditions of operation when inflation is desired, and in which no auxiliary inflating means is needed.

Still another object of this invention is to provide a sail having a chamber inflatable by ram air which Will automatically deflate When operated at very high angles of attack or when running before the wind.

These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawing in which:

Brief description of the drawing FIGURE 1 is a side elevational view of a boat utilizing sails constructed in accordance with this invention;

FIGURE 2 is an enlarged fragmentary perspective view of the head portion of the jib;

FIGURE 3 is an enlarged fragmentary front elevational view showing the inlet to the inflatable chamber of the jib;

FIGURE 4 is an enlarged transverse sectional view of the chamber provided for the mainsail;

FIGURE 5 is a fragmentary sectional view illustrating an alternate connection of the sail to the mast;

FIGURE 6 is an enlarged fragmentary perspective view of the head portion of the mainsail;

FIGURE 7 is a fragmentary sectional view taken along line 7-7 of FIGURE 6, showing the chamber inlet arrangement;

FIGURE 8 is a side elevational view of a modified sail in which the inflatable chambers have extensions to the leech;

FIGURE 9 is a transverse sectional view taken along line 9-9 of FIGURE 8; and

FIGURE 10 is an e-levational view of a spinnaker utilizing the invention.

Description of the preferred embodiments As shown in the drawing, the invention may be seen in FIGURE 1 as applied to a sloop 10 having a jib 11 and a mainsail 12. The sails 11 and 12 are provided with double walled elongated chambers 13 and 14, respectively, extending along their leading edge portions.

With reference to FIGURES 2 and 3, the jib 11 is made of conventional sailcloth material and is of the customary triangular configuration. The chamber 13 is formed merely as a double thickness of the material of the jib 11, with both the forward and rearward edges of the walls of the chamber being stitched together so that a hollow interior is defined. Thus, the chamber 13 includes Opposed walls 15 and 16 sewn together along their forward edge-s at a seam 17. This seam defines the leading edge of the sail. The rearward edges of the walls 15 and 16 also are sewn together along a seam 18 so as to 4 provide the chamber 13 with a hollow interior. The wall 15 of the chamber 13 extends aft from the seam 18 to define the main portion of the jib 11. The chamber 13 runs spanwise of the jib 11, which positions it in a generally vertical direction when the sail is in use with the forward edge 17 of the chamber adjacent the stay 20.

The rearward edge 18 of the chamber 13 preferably is arcuate in shape, extending from a point of connection with the forward edge 17 at both the top and bottom ends of the chamber. The curve of the trailing edge 18 of the chamber approaches that of a parabola or catenary. The trailing edge 18 is arranged so that the maximum chamber width or chord is located at approximately one-third the height of the sail 11. The chamber may extend in width for about 25% to 50% of the chord of the sail.

At the top of the chamber 13 is an inlet opening 22. This is defined by the forward edges of the walls 15 and 16 which are not stitched together at the upper portion of the sail 11 where the opening is located. In order to prevent collapsing of the opening and to assure that dynamic pressure may enter the chamber 13, stiffening is provided to cause the opening 22 always to assume the generally oval shape illustrated. Therefore, there is a stiffener 23 circumscribing the edge of the opening 22, and it is possible also to include a transverse rib 24 extending across the opening.

The chamber 14 for the mainsail 12. is of the same general shape as that of the chamber 13 of the jib 11. Thus, the chamber 14 includes opposed side walls 25 and 26 of flexible sailcloth extending vertically at the luff portion of the sail. The rearward edge 27 where the walls 25 and 26 merge is arcuate, as before, preferably with its maximum chord occurring at approximately one-third the total height of the sail. The rearward edge 27 of the chamber 14 meets the forward edge 28 both at the top and at the bottom of the chamber.

The sail is attached to the mast 29 by any of several known means such as shown in FIGURE 4, depicting a sail provided with a boltrope 30 received in a slot 31 in the mast. Alternatively, as shown in FIGURE 5, the sail may be looped loosely around the mast, with the mast 32 extending inside the chamber 14 at its leading edge. Both of these arrangements are commonly employed on certain types of boats. It is to be noted that the mast is required as a structural member only, and does not perform any of the functions of the invention. Normally, the presence of the mast results in drag and other degradation in the aerodynamic performance of the sail. However, as a result of the presence of the inflated chamber 14, either containing or in close proximity behind the mast, these adverse consequences are lessened. Moreover, the inflated chamber has a thickness generally greater than that of the mast, with the point of maximum thickness at some distance behind the mast. This acts to offset the adverse aerodynamic effects of the mast to a greater extent than would be the case if the chamber were not inflated, in which case the maximum thickness point would be at the mast itself.

Instead of a single opening as illustrated for the jib 11, the mainsail 12 is provided with pairs of openings in its sides, each with an air scoop. This avoids inter- 1fjerence from the mast in providing an inlet to the cham- As illustrated in FIGURES 6 and 7, small scoops 33 and 34 are secured to the walls 25 and 26 of the chamber 14, respectively. The scoops 33 and 34 may be of semirigid material, such as an appropriate plastic which will retain its shape but may be deflected without damage during handling. The scoops 33 and 34 include marginal flanges 35 and 36, which are stitched to the material of the Walls 25 and 26 in forming the attachment of the scoops to the sail. The walls 25 and 26 are provided with openings 37 and 38 inwardly of the scoops 33 and 34. lThis provides communication to the interior of the chaminwardly of the openings 37 and 38 there may be included a valving arrangement to assure that all the air entering one opening applies pressure to the chamber 14 and does not exhaust through the other opening. This may be accomplished by flapper valves 39 and 44), made of the same material as the remainder of the sail. They are simply pieces of material that are sewn to the walls of the chamber adjacent their forward edges 41 and 42, leaving their rearward edge portions free. The valves 39 and 40 operate to prevent air from flowing out of one opening during the time that the other opening is in a position to receive the wind. Thus, for example, if the wind is coming from a direction such that it enters the scoop 33 while the scoop 34 is on the leeward side, the air will enter the chamber 14 through the opening 37, deflecting the flapper valve 39 away from the opening 37. The valve member 39 moves in this manner because the pressure against it from outside the chamber exceeds the pressure within. At the same time, the pressure within the chamber, which is greater than the pressure on the lee side, will cause the flapper valve 40 to lie against the periphery of the opening 38, covering the latter aperture so that the air does not exhaust through the opening 38.

The valves 39 and 40 also assure that air does not exhaust through both of the openings due to a momentary fluctuation in wind velocity. This may occur when the wind dies down briefly and in the absence of the valves the chamber would begin to deflate as air would flow simultaneously out of the openings 37 and 38. This feature of the pressure-responsive valve makes it desirable to include such a valve in other embodiments of this invention, such as providing a flapper valve for the opening 22 of the design of FIGURES 2 and 3.

Therefore, the chamber is maintained sealed except for the opening that receives the wind force. The scoops, by projecting outwardly on either side of the chamber 14, extend beyond the width of the mast so that a scoop always is positioned to receive the wind from whatever direction it is blowing. The provision of the air scoops for the chamber inlet is equally usable on the jib 11 or any other sail mounted on a stay rather than a mast or on a spinnaker.

In use of the boat 10, air enters the chamber 13 by flowing through the opening 22 at the head of the jib 11. Similarly, air enters the chamber 14 through either the scoop 33 and the opening 37 or the other scoop 34 and opening 38, depending upon the direction of the flow of wind. The inlets to both chambers, by being integral with the sails, always point in a proper direction to receive the 'wind force. The normal use of the sails automatically will direct the inlets toward the wind to receive the pressure for inflating the chambers.

By being located at the heads of the sails 11 and 12, the chamber inlets also receive the air at the locations of highest dynamic pressure upon the sails. This is in view of the velocity gradient that occurs with increasing proximity to the surface.

The force of the wind entering the chambers 13 and 14 distends the chambers so that the side walls separate and the chambers assume the contour illustrated in FIG- URE 4. The combination of the internal pressure of the chambers together with the other loads imposed on the sails causes the chambers to assume the elongated but rounded cross-sectional shape shown. Consequently, the inflated chambers 13 and 14 have approximate airfoil configurations, which is desirable for the contour of a sail. This provides generally improved performance for the sail.

With the chambers utilized in this manner. lufling of the sails virtually is eliminated. For example, in a closehauled condition with a low angle of attack to the wind, lufling ordinarily would occur as the pressures on the leeward side approach that on the windward side at the leading edge portion of the sail. However, the pressure within the chambers 13 and 14 always will remain greater than the pressure on the leeward side even during a closehauled condition. Thus, the chambers 13 and 14 remain inflated, and the material maintains its contour and does not flap or flutter. Similarly, if the sail is unloaded to reduce heeling in a high wind, the pressure within the chambers again exceeds that on the lee side so that lufiing does not occur. This means that the boat may be sailed in conditions that otherwise would be undesirable or impossible, while still avoiding a luffing condition. Considerable improvement in performance results and the boats potential speed is increased. Moreover, by being of flexible material, normally the same as for the remainder of the sail, the inflatable chambers impose no weight penalty, and are easily constructed, handled and maintained as well.

The chambers 13 and 14 are given their curved rear edges 18 and 27 to locate the inflated portions at the precise areas of the sail which are subject to the lufiing condition. Also, this provides the chambers with appropriate shapes so that any stress wrinkles in the sails will not intersect the chambers. In particular, at the lower portion of the chamber 14 on the mainsail 12, movement of the boom 43 could cause the chamber walls to wrinkle and resultin distortion of the chamber if the chamber were of finite width at its lower end. With the chamber forward and rearward edges intersecting adjacent the boom, however, the boom may swing around its connection to the mast with no appreciable effect on the shape of the chamber. In addition, by tapering toward the heads of the sails, the chambers 13 and 14 avoid any interference with existing battens that may be provided in the sails at the leech. The chamber sahpes resulting from the curved rearward edges also have aesthetic advantages by being graceful and attractive shapes.

Provision also may be made for varying the chord of the inflatable chambers 13 and 14 at the leading edges of the sails 11 and 12. This allows the chambers to be made shorter lengthwise of the boat and at the same time becoming thicker, which may be used for obtaining special results to enhance the performance of the vessel. This arrangement is illustrated in conjunction with the chamber 14 of the mainstail 12, but could be applied as well for the jib 11 or any other sail. In accomplishing this control, there is a second row of stitching 44 extending through the wall 26 parallel to stitching at the rearward edge 27 of the chamber 14. This defines a narrow passageway along the rearward edge of the chamber, through which extends a halyard 45. The halyard 45 is attached to the material of the sail at it upper end, but extends outwardly from the bottom end of its passageway at the lower edge of the chamber adjacent the boom 43. Control of the chord of the chamber is effected simply by pulling on the exposed portion of the halyard 45, shortening its length and thereby moving the rearward edge 27 of the chamber closer to the forward edge 28. This changes the contour of the side walls 25 and 26, bulging them outwardly to a greater degree. The effect of the wind on the sail at the leading edge of the sail is controlled in this manner.

The chambers may be modified to meet particular conditions or to achieve specific results. For example, as shown in FIGURE 8, the sail 46 includes a chamber having extensions running fore and aft from the region of the luff to the leech of the sail. The main part of the chamber 47 of the sail 46 may be generally similar to the chambers 13 and 14 described above. It is provided, however, with relatively narrow extensions 48, 49, 50, 51 and 52 extending horizontally to the aft edge of the sail 46. These extensions are also of double wall thickness, so that they become inflated along with the main chamber portion 47. The presence of the extensions 48, 49, 5t), 51 and 52 results in stiffened areas throughout the chord of the sail. Flutterin-g and collapse of the sail material is prevented at the leech as well as at the luff through the use of this arrangement.

The arrangement of this invention also is usable on different kinds of sails. In FIGURE 10, the invention is illustrated as applied to a spinnaker 53. Here, the dual thicknesses are arranged so that there is an inflatable chamber portion 54 along the margin of the sail 53. Also there are interconnecting portions 55, 56 and 57 that likewise inflate and impart rigidity to the sail. Openings 58, 59, 60 and 61, provided with flapper valves as previously described, are positioned to point into the wind as the spinnaker is in use. By employing the inflatable chamber principle for the spinnaker 53, the sail presents a larger deployed area when running before the wind. It also renders the spinnaker more eflicient in a reach and, as before, the entering edge of the sail is precluded from lufling through the rigidity provided by the inflated chamber 54.

The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

What is claimed is:

1.. A sail comprising a sheet of flexible material attachable to a support for receiving the impact of wind thereon,

an inflatable chamber integral with said sheet,

said sheet having a forward end and a rearward end,

said chamber having opposed side walls of flexible sheet material distensible to define a contoured exterior,

and an exposed opening means integral with said chamber,

said opening means being positioned to face substantially in the direction of said forward end to receive ram air during the normal use of said sail.

2. Asail comprising a sheet of flexible material attachable to a support for receiving the impact of winds thereon,

said sheet having substantially the configuration of a spinnaker,

said sheet having peripheral edge portions including opposed side walls of flexible material defining an inflatable chamber extending around said edge portions,

said sheet including portions of single thickness beyond said chamber inwardly of said edge portions,

and exposed opening means integral with said chamber,

said opening means facing outwardly of said chamber at said edge portions for receiving ram air for inflating said chamber during the normal use of said sheet of flexible material as a spinnaker. 3. A device as recited in claim 2 in which said chamber includes additional portions extending across said sheet and connecting to said chamber along said peripheral edge portions. 4. A device as recited in claim 1 including in addition valve means associated with said opening means for closing said opening means when the pressure within said chamber exceeds the pressure exteriorly thereof adjacent said opening means.

5. A device as recited in claim 1 in which said opening means includes at least two apertures communicating with the interior of said chamber,

and including valve means for closing either of said apertures when the pressure within said chamber exceeds the pressure exteriorly of said chamber adj acent said aperture.

6. A device as recited in claim 1 in which said chamber is disposed at said forward end, and runs lengthwise thereof,

said chamber having a forward and a rearward edge,

said rearward edge approaching said forward edge at the ends of said edges.

7. A device as recited in claim 6 in which said chamber includes extension means extending from said rearward edge of said chamber to a position adjacent said rearward end of said sheet.

8. A device as recited in claim 7 in which said extension means includes a plurality of relatively narrow portions extending substantially horizontally from said chamber.

9. A device as recited in claim 6 including in addition means for reducing the width of said chamber.

16. A device as recited in claim 9 in which said means for reducing the width of said chamber includes a passage means at said rearward edge of said chamber,

and a filamentous member in said passage means,

said filamentous member being fixed relative to said chamber adjacent the upper portions thereof, and extending outwardly of said passage means at the lower portion thereof,

whereby tension imposed on said filamentous member causes said rearward edge of said chamber to be moved toward said forward edge thereof. 11. A sail comprising a sheet of flexible material attachable to a support for receiving the impact of wind thereon,

said sheet having a forward and a rearward end, a chamber at the forward end of said sheet,

said chamber including a pair of opposed flexible side walls having forward and rearward edges, and means attaching together said forward edges of said side walls and said rearward edges of said side walls, respectively, to provide forward and rearward edges of said chamber,

said forward chamber edge being substantially straight, said rearward chamber edge being arcuate and extending to a position of juxtaposition with said forward chamber edge at the end portions of said edges of said chamber, and opening means at the upper portion of said chamber substantially facing said forward end of said sheet for introducing ram air into said chamber during the use of said sail for effecting inflation of said chamber.

12. A device as recited in claim 1?. in which said chamber has its maximum width at approximately one-third of the total height of said sheet.

13. A device as recited in claim 11 in which the maximum width of said chamber is approximately percent to 50 percent of the maximum width of said sheet between said forward end and said rearward end thereof.

14. A device as recited in claim 11 in which said opening means comprises an aperture at said forward edge of said chamber, and

stiffening means at said aperture for holding said aperture open.

15. A device as recited in claim 11 including in addition valve means associated with said opening means for closing said opening means when the pressure within said chamber exceeds the pressure exteriorly thereof adjacent said opening means.

16. A device as recited in claim 11 in which said opening means includes a duality of scoops,

6 one of said scoops being attached to one of said side walls of said chamber, the other of said scoops being attached to the opposite side wall of said chamber,

said scoops having inlets facing said forward 7O edge,

each of said side Walls having an aperture therethrough inwardly of the scoop attached thereto for receiving air from said scoop and transmitting such air to said chamber.

17. A device as recited in claim 16 including in addition valve means for closing one of said apertures when the other of said apertures is receiving air for inflating said chambers. 18. A device as recited in claim 17 in which said valve means includes a duality of pressure-responsive movable members,

' one of said movable members being attached to said one side wall adjacent said aperture therethrough,

the other of said movable members being attached to said opposite side wall adjacent said aperture through said opposite side wall,

each of said movable members being movable to a position in which it engages the periphery of the side wall to which it is attached around the aperture therethrough for thereby closing said aperture in response to pressure thereon in said chamber greater than pressure thereon exteriorly thereof,

each movable member being movable away from the aperture of the side wall to which it is attached in response to pressure thereon from the exterior of said chamber greater than the pressure thereon in said chamber.

References Cited UNITED STATES PATENTS 288,819 11/1883 Kraeger 114-103 3,298,346 1/ 1967 Cochran 114-103 FOREIGN PATENTS 445,639 6/ 1927 Germany. 463,701 8/1928 Germany.

FERGUS S. MIDDLETON, Primary Examiner.

T. M. BLIX, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0. 3,391 ,668 July 9, 1968 Joseph Birchill It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown -below:

The reference character "42" in the right-hand portion of Figure 7 should read 44 the reference character "43" in Figure 7 should read 45 Signed and sealed this 1st day of September 1970.

(SEAL) Attest:

Edward M. Fletcher, J r.

Commissioner of Patents Attesting Officer WILLIAM E. SCHUYLER, IR. 

